Maryann Mannen

Maryann Mannen became president and CEO of Marathon Petroleum in 2024, leading the largest independent petroleum refiner in the United States. Marathon operates 13 refineries across the country with total throughput capacity of approximately 3 million barrels per day, converting crude oil into gasoline, diesel, jet fuel, and petrochemical feedstocks. The company also holds a majority interest in MPLX, a large midstream master limited partnership that operates crude oil and natural gas pipelines, terminals, and processing plants. Marathon's refining system benefits from significant geographic and crude slate diversification — its refineries process both light sweet and heavy sour crude oils, with facilities on the Gulf Coast, Midwest, and West Coast. The company's Galveston Bay refinery in Texas (formed from the Marathon-Andeavor merger) is one of the largest and most complex in the world. Refining margins (the "crack spread" between crude oil and refined product prices) are the primary determinant of Marathon's profitability. Mannen's management of refining utilization rates, capture of favorable crack spreads, capital allocation between growth investment and shareholder returns (Marathon has been one of the most aggressive share repurchasers in the energy sector), and MPLX distribution growth are the primary drivers of the stock.